1. Field of the Invention
This invention relates to down hole analysis of vibrations of a portion of a drill string in a bore hole and particularly to an apparatus and method for detecting and measuring vibrations of the drill bit.
2. Description of the Prior Art
During drilling operations it is often desirable to measure the frequencies and magnitudes of the vibrations of a portion of a drill string and particularly of the drill bit since such information may be utilized, inter alia, to determine the hardness and porosity of subsurface strata through which the bit is cutting and the amount of wear undergone by the bit. Although various devices are known for measuring drill string vibrations, they lack the capability of directly measuring drill bit vibrations and transmitting data describing these vibrations to the surface. Devices are known, for example, which include a transducer and recording apparatus located in the drill string adjacent the drill bit and which make a record of all vibrations experienced by the bit as it bores into the earth, but this information is not available on the surface until the recording apparatus is brought to the surface. It is also known to measure vibrations of the drill string at the surface, but as the bit bores deeper into the earth and the drill string increases in length measurements taken at this location become less representative of drill bit vibrations, because of the attenuation and distortion of these vibrations as they propagate up the drill string.
The primary problem that must be solved to enable real time transmission of data describing drill bit vibrations to the surface is that of transmitting a signal containing a range of frequency components through a medium of non-uniform attenuation without loss of fidelity. Specifically, the vibrations experienced by the drill bit are represented by a complex waveform including many frequency components. Transmission of such a signal to the surface through an available medium such as wiring running the length of the drill string must be accomplished without the distortions normally caused by the medium's attenuation of different frequency components by differing amounts.
It is the primary object of the present invention to overcome this problem and to provide an apparatus and method for down hole detection and measurement of vibrations of a portion of a drill string and for producing signals representative of these vibrations which can be transmitted to the surface without a loss of fidelity.
It is a further object of the present invention to provide such an apparatus which may be remotely controlled to measure vibrations of selected frequencies.